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作者在引入conf/global 文件时，就已经对操作系统的类型进行判断，同时也对DISTRO进行了赋值。
部分代码，如图：
显然文件里的KERNEL_NAME的值就是判断完成的操作系统，具体分析该值是如何得到的。
就是通过命令“uname –s | tr ‘[a-z]’ ‘[A-Z]’得到的，不过作者在此处把小写换成了大写。 接下来分析根据不同操作系统，怎么获得不同的DISTRO值，代码如下：
if [ X"${KERNEL_NAME}" == X‘LINUX‘ ]; then # Directory of RC scripts. export DIR_RC_SCRIPTS=‘/etc/init.d‘ if [ -f /etc/redhat-release ]; then # RHEL/CentOS export DISTRO=‘RHEL‘ # Get distribution version if grep ‘\ 6‘ /etc/redhat-release &>/dev/null; then # version 6.x export DISTRO_VERSION=‘6‘ elif grep ‘\ 7‘ /etc/redhat-release &>/dev/null; then # version 7.x export DISTRO_VERSION=‘7‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi # Get distribution name as DISTRO_CODENAME if grep ‘^Red‘ /etc/redhat-release &>/dev/null; then # RHEL export DISTRO_CODENAME=‘rhel‘ elif grep ‘^CentOS‘ /etc/redhat-release &>/dev/null; then # CentOS export DISTRO_CODENAME=‘centos‘ elif grep ‘^Scientific‘ /etc/redhat-release &>/dev/null; then # Scientific Linux export DISTRO_CODENAME=‘scientific‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi elif [ -f /etc/lsb-release ]; then # Ubuntu export DISTRO=‘UBUNTU‘ # Ubuntu version number and code name: # - 14.04: trusty # - 15.04: vivid export DISTRO_ID="$(grep ‘DISTRIB_ID‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" export DISTRO_VERSION="$(grep ‘DISTRIB_RELEASE‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" export DISTRO_CODENAME="$(grep ‘DISTRIB_CODENAME‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" # Unsupported releases: 12.x, 13.x, 14.10 if echo "${DISTRO_VERSION}" | grep -E ‘^(12|13|14\.10)‘ &>/dev/null ; then export UNSUPPORTED_RELEASE=‘YES‘ fi elif [ -f /etc/debian_version ]; then # Debian export DISTRO=‘DEBIAN‘ # Get major release version number export DISTRO_VERSION="$(cat /etc/debian_version)" # Set distro code name and unsupported releases. if grep ‘^7‘ /etc/debian_version &>/dev/null || grep -i ‘^wheezy‘ /etc/debian_version &>/dev/null; then export DISTRO_VERSION=‘7‘ export DISTRO_CODENAME=‘wheezy‘ elif grep ‘^8‘ /etc/debian_version &>/dev/null || grep -i ‘^jessie‘ /etc/debian_version &>/dev/null; then export DISTRO_VERSION=‘8‘ export DISTRO_CODENAME=‘jessie‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi # Override settings. export SHELL_NOLOGIN=‘/usr/sbin/nologin‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi elif [ X"${KERNEL_NAME}" == X‘FREEBSD‘ ]; then export DISTRO=‘FREEBSD‘ export DISTRO_VERSION="$(uname -r |awk -F‘[.-]‘ ‘{print $1}‘)" # Directory of RC scripts. export DIR_RC_SCRIPTS=‘/usr/local/etc/rc.d‘ export PYTHON_BIN=‘/usr/local/bin/python‘ # Unsupported releases: 7, 8. if echo "${DISTRO_VERSION}" | grep ‘^[78]‘ &>/dev/null ; then export UNSUPPORTED_RELEASE=‘YES‘ fi export SHELL_BASH=‘/usr/local/bin/bash‘ # Default password scheme. export DEFAULT_PASSWORD_SCHEME=‘BCRYPT‘ elif [ X"${KERNEL_NAME}" == X‘OPENBSD‘ ]; then export DISTRO=‘OPENBSD‘ export DISTRO_VERSION="$(uname -r)" # Directory of RC scripts. export DIR_RC_SCRIPTS=‘/etc/rc.d‘ export RC_CONF_LOCAL=‘/etc/rc.conf.local‘ export SHELL_BASH=‘/usr/local/bin/bash‘ export PYTHON_BIN=‘/usr/local/bin/python‘ # Unsupported release: 5.6 and earlier versions. if echo "${DISTRO_VERSION}" | grep ‘^5.[123456]‘ &>/dev/null ; then export UNSUPPORTED_RELEASE=‘YES‘ fi # Default password scheme. export DEFAULT_PASSWORD_SCHEME=‘BCRYPT‘ else # Not support *BSD and other distrobutions yet. echo "Error: Your OS is not supported yet." exit 255 fi
代码比较长，不过脉络比较清晰，首先根据KERNEL_NAME的值判断是哪种操作系统，作者给出的判断是3种，分别是LINUX OPENBSD FREEBSD , 也就是该脚本只能在这3种平台上进行部署，如果需要自己扩展的话，就可以在增加新的判断，最后如果3种都不是的话，就直接返回255，如下代码:
echo "Error: Your OS is not supported yet." exit 255
接下来分析当KERNEL_NAME的值为LINUX，脚本做了什么，首先定义了一个变量
export DIR_RC_SCRIPTS=‘/etc/init.d‘
linux中一般启动脚本都是放在这个目录里的,LINUX本身也有很多版本，因此作者在此处又进行多种类型的判断，判断的依据文件分别是/etc/redhat-release /etc/lsb-release /etc/debian_version这3种文件分别对应rhel/centos ubuntu debian , 从而也说明在LINUX的版本中，只支持这3种，其他的LINUX版本是不支持的，最后作者返回一句代码：
定义了一个UNSUPPORTED_RELEASE变量，在后续的代码应该会调用这个变量来判断是否支持。
针对这3种LINUX，作者又具体细分到不同的小版本中，首先看rhel/centos 系列，下面代码：
首先根据存在redhat-release文件，定义了DISTRO的值
if [ -f /etc/redhat-release ]; then
export DISTRO=‘RHEL‘
这样在get_all.sh的脚本里调用时就有了判断依据，接着判断具体的版本，
if grep ‘\ 6‘ /etc/redhat-release &>/dev/null; then # version 6.x export DISTRO_VERSION=‘6‘ elif grep ‘\ 7‘ /etc/redhat-release &>/dev/null; then # version 7.x export DISTRO_VERSION=‘7‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi
显然只支持6和7两个版本，也就是安装时，如果不是这2个版本的话，就会返回unsupport_release的值为YES了。
rhel还有两个个反编译版本即centos ，Scientific Linux, 因此作者又定义了一个变量来区别 DISTRO_CODENAME, 代码如下:
if grep ‘^Red‘ /etc/redhat-release &>/dev/null; then # RHEL export DISTRO_CODENAME=‘rhel‘ elif grep ‘^CentOS‘ /etc/redhat-release &>/dev/null; then # CentOS export DISTRO_CODENAME=‘centos‘ elif grep ‘^Scientific‘ /etc/redhat-release &>/dev/null; then # Scientific Linux export DISTRO_CODENAME=‘scientific‘ else export UNSUPPORTED_RELEASE=‘YES‘ fi
显然在/etc/redhat-release文件里，不同的发行版本有不同的关键字，这样关于红帽系的操作系统，作者就已经区分完毕了。
接下来关于ubuntu的判断就简单多了，看图
根据/etc/lsb-release的文件是否存在，赋值DISTRO为UBUNTU，然后判断具体版本，看代码
export DISTRO_ID="$(grep ‘DISTRIB_ID‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" export DISTRO_VERSION="$(grep ‘DISTRIB_RELEASE‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" export DISTRO_CODENAME="$(grep ‘DISTRIB_CODENAME‘ /etc/lsb-release | awk -F‘=‘ ‘{print $2}‘)" # Unsupported releases: 12.x, 13.x, 14.10 if echo "${DISTRO_VERSION}" | grep -E ‘^(12|13|14\.10)‘ &>/dev/null ; then export UNSUPPORTED_RELEASE=‘YES‘ fi
从程序可以看出UBUNTU的ID , RELEASE , CODENAME的值都在/etc/lsb-release的文件里，用grep 和awk匹配后，赋予不同变量的值。
用grep 筛选出系统版本为12,13,14.10的都为不支持版本，目前支持的版本为14.04,15.04
iredmail安装脚本分析（三）---conf/global DISTRO值的来源及操作系统的判断
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原文地址：http://www.cnblogs.com/xielinux/p/4881982.html
